Agricultural Pesticides and Wildlifethe
basis for current concerns
This short summary outlines the key areas of
concern relating to the effects of agricultural use of pesticides
and wildlife. Concerns relate to areas of pesticide abuse and
misuse, and to the direct and indirect effects of approved use.
It is clear that whilst there are concerns over current measurable
impacts on wildlife, many of our concerns relate more towards
the lack of understanding of potential risks to wildlife populations.
In part this is because evidence for effects on populations is
difficult to collect. In part also this is because, especially
in the case of indirect effects on farmland bird populations,
pesticide use is only one of several recent changes which is likely
to have contributed towards observed declines. The relative contribution
of pesticides in such cases may be difficult to ascertain, and
the measures to effect a recovery may involve factors in addition
to those tackling pesticide use.
There are four different areas of concern relating
to the impacts of pesticides on wildlife. These are:
direct effects of approved use on
non-target species. This includes both lethal and sublethal effects,
including primary and secondary poisoning, both acting within
the crop and off target (eg in water courses). It includes also
the effect of pesticides alone and in combination with other pollutants;
indirect effects of approved use,
for example through reduction in prey availability to non-target
species, or deterioration in habitat quality;
or incorrect use can lead to inadvertent damage to non-target
use to poison a species in contravention of conditions of use.
3. DIRECT EFFECTS
3.1 Trials have shown direct effects of
pesticides on within-crop populations of invertebrates and wild
plants. Monitoring and wide scale studies have shown long-term
and large scale declines in such groups although these have generally
been less able to show an effect attributable to pesticides alone.
It has been possible to demonstrate recovery in a range of species
where pesticide use alone (reduction in herbicide and insecticide
use) has been manipulated in conservation headlands.
3.2 It is known that sublethal effects may
increase the susceptibility to other mortality factors (such as
predation), interfere with behaviour and reduce reproductive success.
The risk of sublethal effects of a range of pesticide groups on
fish species as well as on aquatic invertebrates are also of concern.
Although population effects have not been demonstrated as a consequence
of sublethal exposure to modern agricultural pesticides in the
UK, this remains an area of poorly evaluated risk.
3.3 The risks to wildlife of interactions
between pesticides, or between pesticides and other pollutants,
is also of concern. Although field evidence is lacking for effects
on wildlife populations of synergism between pesticides, such
effects have been little studied.
3.4 Toxicological and experimental studies
indicate that there are likely to be risks of adverse ecological
effects of pesticides at concentrations found in some surface
waters. However there have been few studies to examine whether
such effects have occurred in the field as a result of agricultural
pesticide use. However the serious consequences for aquatic invertebrates
arising from synthetic pyrethroids entering water courses following
sheep dipping or industrial wool processing have been well documented
in recent years.
A pesticide tax which steered product choice
towards the use of more selective products would have benefits
in reducing risks of some of the direct effects summarised above.
In some cases pesticide management may be as much an issue as
product choice. Measures which reduce drift or leaching into water
courses (application technology, buffer zones) would need encouragement.
4. INDIRECT EFFECTS
The decline in the population of the grey partridge
in the UK since the 1960s is attributed in part to the increasingly
widespread use of herbicides in arable crops, and hence in the
availability of weeds for the invertebrate prey of gamebird chicks.
Greater use of insecticides in cereals is likely to have further
affected chick survival by reducing invertebrate prey availability
in spring. There is convincing evidence that both weed and arthropod
prey densities increase in selectively sprayed field edges (conservation
headlands) which in turn improves partridge survival. Overall,
evidence is accumulating for the existence of mechanisms of indirect
effects operating in several other declining farmland bird species
in a similar way to the grey partridge, although other factors
are likely to play a role and so manipulation of pesticide use
alone may not necessarily be the most effective means of achieving
any reversal. At present, designs for a pesticide tax do not include
consideration of its potential to contribute towards reducing
indirect effects of pesticide use.
Misuse can arise from careless use, including
spillages or overspraying water courses, as well as deliberate
misuse. Certain categories of pesticide are involved more frequently
than others in pesticide misuse incidents affecting vertebrates,
particularly seed and granular treatments and baits including
molluscicides and rodenticides. Although mechanisms, such as a
pesticide tax, which may restrict the number of occasions when
a pesticide is used can reduce the risk of unforseen events (including
some "misuse" events) occurring, it is likely that regulation
and enforcement will remain the major mechanism for tackling this
Pesticide tax is unlikely to play a significant
role in dealing with pesticide abuse or misuse incidents. In other
areas of concern it will have a role provided it is carefully
designed, but we should be clear that it is as necessary to tackle
the way in which pesticides are used as much as what
is used, and alternative policy instruments are likely to be needed